The present invention relates to a gas turbine engine, in particular in the aeronautical field, and is aimed at mounting a rotor shaft inside the engine.
The operations of mounting and demounting a turbine engine are complicated owing to the number of parts which constitute it and of the small clearances between them even though their dimensions may be large. The cost of carrying out work on the engine which comprises such operations is consequently always high. It is therefore constantly sought to simplify them. In a twin-spool, front turbofan engine, such as the cfm56 engine, access to the support bearing of the high-pressure compressor shaft is particularly difficult since it is mounted, at the level of the intermediate casing, to the rear of the fan and of the two first bearings supporting the low-pressure compressor shaft and the fan shaft, respectively. The intermediate casing is that part of the machine casing which particularly supports the front bearings of the rotors. To avoid demounting the entire front part of the engine and of the fan in particular, the elements of this bearing are currently arranged is such a way as to allow mounting from the rear. Such a solution, although advantageous, still has a number of drawbacks which it would be desirable to eliminate.
With reference to FIGS. 1 and 2, a solution corresponding to the teaching of the prior art is reviewed. The engine assembly is not represented, only the immediate surroundings of the bearing being visible. The front and rear are defined with respect to the forward travel direction of the engine. Part of the fixed structure of the intermediate casing 2 is shown, with the ball bearing 3 of the HP compressor shaft being supported by its outer race in this fixed structure. The bearing rotationally supports the front end of the HP compressor shaft 4, of which the journal 4′ and a rotor disk 4″ can be seen. The bearing supports at its front a bevel gear 5 which drives the gear 5′ connected to a radial shaft, forming the inlet gearbox (IGB) used to drive the auxiliary equipment: pumps, electrical current generators or the like. The bevel gear meshes, for this purpose, with the gear of the radial transmission shaft which is housed in one of the radial arms of the intermediate casing so as to drive the gears of the accessory gearbox (AGB). The bevel gear is fixedly connected to the cylindrical sleeve supported by the bearing.
To maintain the shaft 4 in the bearing 3, a nut 6 is provided according to the prior art and is retained inside the gear 5, at the upstream end, by a segment or snap ring 6′. The nut comprises a thread on its external surface by means of which it is screwed inside the upstream end of the shaft 4, this end being provided with a suitable thread. A nut retainer 6″, which is secured against rotation by axial splines in the shaft 4 and has flexible tabs which lock into a circular groove in the shaft 4, prevents the nut from accidentally loosening. Furthermore, axial splines on the internal wall of the sleeve of the gear 5 cooperate with splines on the external surface of the shaft 4 to prevent any rotation of one with respect to the other. This mounting incorporates the auto-extraction function of the HP compressor. The function is provided by the segment which axially secures the bearing nut to the bevel wheel. Thus, by screwing the nut into the thread of the HP compressor shaft, the compressor is mated with the bearing; conversely, by unscrewing the nut, the compressor is pushed away rearwardly since the nut is blocked axially by the segment.
FIG. 2 shows the bearing before the shaft 4 is mounted. The nut, arranged in front of the bearing, is mounted beforehand on the gear before any mounting of the elements from the rear of the intermediate casing. To prepare for the mounting of the shaft 4, the bearing 3 is heated at C in order to expand it and minimize the shrinkage forces. To avoid heating the nut 6 and minimize the friction in the thread when tightening it on the shaft 4, a thermal protection P is placed around the nut. However, this protection is complicated to implement. It cannot be installed effectively.